No abstract

short review of basic definitions relating to the term "tectum" is given. Pollen grains with a teclum prforatum are described and defined. A new term "microreticulate", is proposed for describing exine structures which consist of minulc reticula with thin muri ( < 1 p in breadth) encompassing small lumina (c 1 p in diameter).The term "reticulate" is lo be restricted to reticulate exines sensu stricro. i.e.. provided with distinct muri.frequently about 1 / L or more in breadth, and with lumina larger than 1 in diameter.

Praglowski, J. (The Palynological Laboratory of the National Science Rexarch Council). The po//efi niorphology oj the Haloragacrar with rrjereiice to taxorioriip. Grana 10: 159-239, 1970.-Pollen morphological investigations of the family Haloragaceae were carried out using light microscopy supplemented by electron microscopical studies. An attempt was made to correlate the pollen morphology with the taxonomy of th: family. The pollen morphological data provide clear support in favour of the division of the family into two separate families, respectively, Ihloragaceae and Gunneraceae. noth subfamilies, it., Haloragoideae Schindl. (excluding a few species in the subsection Spongiocarpus Schindl.) and Gunnxoideae Schindl., are stenopalynous. Important arguments concerning pollen morphology, gross morphology, ecology, and type of pollination, favour a regroup-MATERIAL AND hlETHODS A. Lnboratory work Only polliniferous material from herbarium specimens was used in this investigation. The material was obtained from the following herbaria: AD,

In Onagraceae, pollen is shed in mature tetrads in most Epilobieae, many species of Ludwigia (Jussiaeeae), and two closely related species of the large genus Camissonia (Onagreae). Mature tetrads of Camissonia cardiophylla and representative species of Epilobium and Ludwigia were examined with light, scanning, and transmission electron microscopes. Morphological diagnoses of monad units indicated that individual taxa could be readily distinguished. Statistical analyses of tetrads which remained after acetolysis treatment revealed significant differences in the strength of the binding mechanisms. Mechanisms of tetrad cohesion were found to consist of two principal types. Common to all taxa is cohesion of pollen wall surfaces at the aperture margins; this mechanism is well known in many angiosperm groups. With the exception of Camissonia, the remaining taxa also display binding by means of short exine fragments between adjacent pollen units. These fragments, termed bridges and reported here for the first time, are located in the area extending from the aperture margins to near the center of the proximal exine faces. Thin sections reveal that layers of the bridges are identical with those of the exine. Comparisons were made between bridges and viscin threads, both of which occur on the proximal faces of the grains. Viscin threads are present on all pollen grains in Onagraceae and exhibit distinctive morphologies, and bridges were viewed morphogenetically as related to viscin threads but including an endexine layer and occupying a position near the apertures where cohesion of wall surfaces also occurs. In an evolutionary sense, the formation of mature tetrads almost certainly occurred independently in Camissonia and may have done so in Ludwigia and the Epilobieae.